1. Field of the Invention
The present invention relates to a vacuum pump and a method of manufacturing a vacuum pump.
2. Description of the Related Art
Conventionally, there has been used a vacuum pump such as a turbo-molecular pump for chamber evacuation in a semiconductor manufacturing apparatus, a liquid crystal manufacturing apparatus, or the like. In an etching process performed by a semiconductor manufacturing apparatus or a liquid crystal manufacturing apparatus, reaction products are disadvantageously deposited on a vacuum pump. In view of this, there is known a method of increasing the temperature of a pump by heating means to suppress deposition of the reaction products. For example, in a vacuum pump disclosed in JP 2011-80407 A, since reaction products are likely to be deposited on an exhaust unit which includes a cylindrical rotor and a stator (screw stator), a heater is embedded in the stator to directly heat the stator to increase the temperature of the stator.
In a vacuum pump in which a rotor rotates at high speed with a tiny gap with respect to a stator, it is necessary to concentrically arrange the rotor and the stator. Thus, when the stator is fixed to a base, a shaft section of the stator and a hole of the base are allowed to have a fitting relation with a clearance of approximately 0.1 mm in the fixing part to position the stator.
However, when a heater is disposed on the stator to heat the stator as described above, the clearance becomes smaller due to thermal expansion, which causes the entire circumference of the shaft section to come into contact with the hole. As a result, heat of the stator having high temperature disadvantageously escapes to the base having low temperature to thereby decrease the temperature of the stator.